Keyboard switch for desk top electronic calculators

ABSTRACT

There is provided a keyboard switch for desk top electronic calculators in which a conductive member and a plurality of tubular resilient means are disposed between fixed electrode means formed on a printed circuit board and a plurality of key buttons, whereby the positive contacting action between the fixed electrode means and the conductive member by the operated key button and the self-restoration of the operated key button are ensured by the associated tubular resilient means.

United States Patent 1191 Nakamura et al. Oct. 7, 1975 [54] KEYBOARDSWITCH FOR DESK TOP 2.848.920 8/1958 Lester 200/ I66 C ELECTRONICCALCULATORS 3,304,386 2/1967 Shlesinger. Jr. 200/83 B 3,668,337 6/1972Sinclair 200/5 A [75] Inventors: Shigeo Nakamura, Neyagawa; 3,742,1576/1973 Leposavic 200/159 B Yutaka Takano, Katano; Masaki 3,743,7987/1973 Pentecost 200/5 R Suzumura; Keizi Onishi, both of 3.773.99811/1973 Seegar et al..... 200/159 B Moriguchi a" of Japan Klehm, J1 B[73] Assignee: Matsushita Electric industrial Co., Ltd., Osaka, JapanPrimary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith[221 Filed 1973 Attorney, Agent, or Firm-Stevens, Davis, Miller & [21]Appl. No.: 389,436 Mosher [30] Foreign Application Priority Data Feb.20, 1973 Japan 48-20938 [57] ABSTRACT 2% 12:: There is prov1ded akeyboard switch for desk top elec- 1973 g 48 37336w] tronic calculatorsin which a conductive member and 1973 1a an 48 38403[U] a plurality oftubular resilient means are disposed bep tween fixed electrode meansformed on a printed cir- [52] U S cl zoo/5 ZOO/159 ZOO/264 cuit boardand a plurality of key buttons, whereby the [51] HOIH 13/52 positivecontacting action between the fixed electrode [58] Fieid 159 B 5 A meansand the conductive member by the operated ZOO/5 E 6 5 key button and theself-restoration of the operated key button are ensured by theassociated tubular resilient [56] References Cited means UNITED STATESPATENTS 8 Claims, 17 Drawing Figures 2.025.981 12/1935 Getty 200/159 B iUS. Patent OM1 sheet 1- 4- $911,233

FIG. lo FIG-lb PRIOR ART U.S. Patent 'Oct. 7,1975 Sheet2 on 3,911,233

US. Patent Oct.7,1975 Sheet3of4 3,911,233

US. Patent Oct. 7,1975 Sheet4 of4 3,911,233

KEYBOARD SWITCH FOR DESK TOP ELECTRONIC CALCULATORS The presentinvention relates to a keyboard switch which is of a compact and thinconstruction and which produces no chattering noise.

The size of desk top electronic calculators has been reduced and thecalculators made more compact as a result of the miniaturization oftheir display and circuitry sections made possible by theminiaturization of electronic components through the development ofintegrated circuits or large scale integrated circuits. Particularly, inthe field of desk top electronic calculators, the tendency has changedtoward a general adoption of handy-type desk top electronic calculatorswhich can be carried in ones pocket. In view of these circumstances,there has naturally existed a need for a keyboard switch of compact andthin structure which is used by the operator to enter the necessaryinformation for continuous computational operations.

Further, there has been a general adoption of MOS elements forconstructing desk top electronic calculator; these circuits have a highimput impedance and therefore it is possible to use a mechanical switchfor entering signals whose contact resistance is very high.

The purpose of the present invention will be made apparent byconsidering the drawbacks of conventional switch structures of the abovetype with reference to the accompanying drawings, in which:

FIGS. 1a and 1b are a front sectional view and side sectional view of aprior art keyboard switch of the reed switch type;

FIG. 2 is a front sectional view of another prior art keyboard switchemploying a metallic movable contact piece;

FIG. 3 is a front sectional view of still another prior art keyboardswitch using a conductive plastic sheet;

FIG. 4 is an exploded perspective view showing an embodiment of akeyboard switch according to the present invention;

FIGS. 5a to 5d are partial sectional views of the keyboard switch ofFIG. 4 which are useful for explaining the operation thereof;

FIGS. 6a to 6d are longitudinal and cross-sectional views showingvarious forms of the tubular resilient means used in the keyboard switchshown in FIG. 4;

FIG. 7 is a partial sectional view of another embodiment of the presentinvention;

FIG. 8 is a sectional view showing the tubular resilient means used instill another embodiment of the present invention; and

FIGS. 9a and 9b are a partial perspective view and partial sectionalview showing a tubular resilient means formed integral with a sheet instill another embodiment of the present invention.

One of the keyboard switches known in the art is the reed switch type inwhich, as shown in FIGS. 1a and 1b, a reed switch element 2 is attachedto a printed circuit board 1 and a key button 4 which is guided by aframe 3 and the printed circuit board 1 to move vertically is providedwith a magnet 5 and a spring 6 which restores the key button 4. Adisadvantage of the reed switch type is that the size of the reed switchelement 2 itself constitutes a limiting factor in the miniaturization ofthe keyboard switch and moreover a large stroke is required for thevertical movement of the key button 4 thus constituting another limitingfactor in reducing the size and thickness of the keyboard switch. Thisreed switch type is also disadvantageous from the manufacturing costpoint of view, since the reed switch element 2 itself is expensive tomanufacture.

As a substitute for the reed switch type keyboard switch, anotherkeyboard switch has been developed and used in which, as shown in FIG.2, a metallic movable contact piece 9 is provided to cooperate with afixed electrode 8 formed on a printed circuit board 7 and the movablecontact piece 9 is actuated by a key button 12 fit in a frame 10vertically movable through a spring 11.

Still another type of keyboard switch has been developed and used inwhich, as shown in FIG. 3, an insulating spacer 15 is disposed on fixedelectrodes 14 formed 'on a printed circuit board 13 and a conductiveplastic sheet 16 is placed on the insulating spacer 15, whereby theconductive plastic sheet 16 is pressed to contact with the fixedelectrodes 14 by a keyboard switch 19 fit in a frame 17 through a spring18.

These two types of keyboard switch are also disadvantageous in thatsince the movable contact piece 9 or conductive plastic sheet 16 ismoved in a vertical direction with respect to the fixed electrode 8 or14, the switch is turned on when the key button 12 or 19 is near thelowermost point of its downward movement with the result that a verysmall clearance is left after the turning on of the switch and thereforea positive depression of the key button must be maintained throughoutthe whole stroke to operate the switch. Moreover, when the key button 12or 19 starts restoring from its lowermost position, the resiliency ofthe spring 11 or 18 and that of the movable contact piece 9 orconductive plastic sheet 16 oppose each other causing a resonance orbounce at the portions of their contact and thereby frequently inducingchattering which is a ruinous disadvantage for the keyboard switch.

In other words, these deficiencies have a direct effect on the operatingquality of the key buttons by the operator, giving rise to erroneousoperations with considerable deterioration in the reliability anddurability of the desk top electronic calculator. Moreover, the use ofsuch keyboard switches is costly since they generally require manycomponent parts and much labor for their assembly.

The present invention contemplates the elimination of these deficienciesof the prior art devices, and it is therefore an object of the presentinvention to provide a keyboard switch which is of compact and thinstructure and which thus greately contributes to the miniaturization ofdesk top electronic calculators.

It is another object of the present invention to provide a keyboardswitch which operates with increased stability without chattering toensure a greater reliability and durability of desk top electroniccalculators.

It is still another object of the present invention to provide akeyboard switch which is simple in construction requiring a reducednumber of component parts, inexpensive to manufacture and easy tooperate.

The construction and features of the present invention will now beexplained with reference to FIGS. 4 through 9.

Referring first to FIG. 4, the detailed construction of a keyboardswitch according to an embodiment of the present invention will bedescribed. In FIG. 4, numeral 20 designates a frame made for example ofa synthetic plastic on which a fixed number of key buttons 21 aremounted and which is formed with a through hole 22 for each key button21 to guide its vertical movement. A plurality of tubular resilientmeans 23 made of resilient synthetic plastic are disposed below themounted key buttons 21, and positioning notches 24 for the tubularresilient means 23 are cut in the inner peripheral wall portions of theframe 20 and partition wall portions 25. Each of the key buttons 21 isalso formed on its periphery with n'otches 26 for receiving the tubularresilient means 23 and it is further provided with a semisphericalprojection 27 on the central lower actuating surface thereof. Disposedbelow the tubular resilient means 23 is a flexible sheet 28 made of amaterial mixed with powder of conductive substance, for example, carbonblack, and disposed below this conductive sheet 28 is an insulatingspacer 30 which is made for example of a synthetic plastic of apredetermined thickness and which is formed with as many holes 29 asthere are the key buttons 21 at the positions corresponding to the keybuttons 21, which holes have a shape desired from the viewpoint ofdesign. A substrate in the form of a printed circuit board 32 formedwith fixed electrodes 31 by a printed-circuit technique is disposedbelow the insulating spacer 30 and this printed circuit board 32 issecured to the frame 20 with small screws 33 thereby securely holdingtherebetween the key buttons 21, the tubular resilient members 23, theconductive sheet 28 and the insulating spacer 30.

With the construction described above, the operation of the keyboardswitch will be explained with reference to FIGS. a to 5d.

FIG. Sashows the conditions in the keyboard switch when none of the keybuttons is operated. When one of the key button 21 is depressed with afinger, the key button 21 is guided by the hole 22 in the frame to movedownward so that, as shown in FIG. 5b, the tubular resilient means 23 isgradually pressed and deformed by the semi-spherical projection 27.Namely the tubular resilient means 23 is deformed through two steps,through the first step of which the cross section of said means takesthe form of an ellipse and through the second step of which said meansbegins to deform downward due to its repellent force. Consequently theconductive sheet 28 disposed in close contact with the lower part of thetubular resilient means 23 is pressed into the corresponding hole 29 ofthe insulating spacer 30.

when this operation is continued, the tubular resilient means 23 isdownwardly deformed by the semispherical projection 27 of the key button21 so that the conductive sheet 28 is eventually brought into contactwith the fixed electrodes 31 on the printed circuit board 32 as shown inFIG. 50 thereby closing the circuit.That is, the switch is turned on.

When the key button 21 is depressed further, the switch remains in theclosed position as shown in FIG. 5d. The downward stroke of the keybutton 21 is so designed that the downward motion of the key button 21is stopped at or before a position where the tubular resilie nt means 23is completely depressed.

When the depression of the key button 21 is released, the deformedtubular resilient means 23 returns to its original form by its ownresilient property and this restora tion causes the key button 21 tomove upward and return to the position shown in FIG. 5a. The conductivesheet 28 depressed by the tubular resilient means 23 returns to itsoriginal position by its own resiliency along with the restoration ofthe tubular resilient means 23, thereby interrupting the contact betweenthe conductive sheet 28 and the fixed electrodes 31 and turning theswitch off.

Further, tubular resilient means 23 having various shapes may beemployed. That is, it may be of cylindrical shape having the same wallthickness throughout its length as shown in FIG. 6a or of cylindricalshape with the wall thickness thicker on the key button side as shown inFIG. 6b. Alternatively, it may be formed to have a rectangular sectionas shown in FIG. or a trangular section as shown in FIG. 6d. Thus, theshape of the tubular resilient means 23 may be selected as described.

Furthermore, as shown in FIG. 7, a conductive tubular resilient means 34prepared from a resilient synthetic plastic mixed with a powder of aconductive substance, e.g., carbon black to make it conductive may beused in place of the tubular resilient means 23 and the conductive sheet28 thereby serving the purpose of two component parts with a singlecomponent part. Still furthermore, the tubular resilient means may bemade partially conductive instead of making it entirely conductive.

The tubular resilient means 34 may also be formed, as shown in FIG. 8,with projections 35 on the lower side thereof to serve as spacers sothat in assembling the tubular resilient means 34, each of theprojections 35 having an insulating sheet attached on the bottom sidethereof may be disposed on the printed circuit board 32 or theprojections 35 may be integrally formed with the conductive tubularresilient means 34 in such a manner that only the projections are madenonconductive. Further, no care is needed for the determination of theinsulating property of the projections 35, providing that the printedwiring of the printed circuit board is well-designed or patternedtherefor to connect the fixed electrodes. Accordingly it is unnecessaryto provide the nonconductive, i.e., insulating sheet, so that theoverall portion of the projections can be made of the same material asthe tubular means. The tubular resilient means constructed by either ofthese two methods may concurrently serve as a tubular resilient member,conductive sheet and insulating spacer.

Further, as will be seen from FIGS. 9a and 9b, a resilient insulatingsheet 36 may be integrally formed with tubelike portions 37 and recessedportions 38 may be formed on the lower side of the insulating sheet 36facing the fixed electrodes 31 on the printed circuit board 32 so thatthe tubelike portion 37 is located at the center of a thin portion 39provided by the recessed portion 38 and at least the tubelike portions37 become conductive. The insulating sheet 36 thus produced mayconcurrently serve as a tubular resilient member, conductive sheet andinsulating sheet. I

The keyboard switch of the present invention constructed as abovedescribed can, by virtue of the use of tubular resilient means, have asufficient clearance to permit the key button to move downward furthereven after the closing of the circuit. This well suits the mentalfeeling of a man and constitutes a factor which has an important effecton the operating quality of the keyboard switch, that is, the operatingquality of the keyboard switch can be improved greatly.

Further, since the conductive sheet adapted to contact with the fixedelectrodes is resilient, its engaging and disengaging operations,coupled with the elastic force of the tubular resilient, can provide aclearance for the movement of the key button and therefore the bounce atthe contacting area can be absorbed to prevent the occurrence ofchattering or resonance. The keyboard switch is thus free frommisoperation and highly reliable and durable.

Further, the use of the resilience of the tubular resilient means andthe conductive sheet to provide the necessary restoring force for thekey button has the effect of eliminating the use of any coil spring orthe like as in the conventional keyboard switches and thereforesimplifying the structure.

Still further, since the thickness of the component parts, i.e., thetubular resilient means, conductive sheet, insulating spacer, printedcircuit board, etc. needs not be greater than that required to ensuretheir mechanical strength and functions, the -thickness of thesecomponent parts can be generally minimized. For example, the entirethickness of one keyboard switch according to the present invention canbe made 7.0 mm by using tubular resilient means of 2.5 mm in diameterand selecting the stroke of the vertical movement of the key buttons at1.5 mm, thereby reducing the size and thickness of the entire structureto the maximum possible extent that would not cause any inconvenience tothe operation of the keyboard switch by the operator.

Further, it should be appreciated that the keyboard switch according tothe present invention, by virtue of a reduction in the number ofcomponent parts and the use of a component part combining the functionsof a tubular resilient member and conductive sheet in one or combiningthe functions of a tubular resilient means, conductive sheet andinsulating spacer in one, can ensure a reduction in the number ofcomponent parts and an increased productivity owing to the simplifiedassemblying with resultant considerable reduction in the manufacturingcost.

It should also be appreciated that by virtue of the use of tubularresilient means, there is no large variation in the operating forcethrough the entire range of the key button stroke, that is, thevariation in the pressing force according to the amount of thedeformation of the tubular resilient means is small as compared with acoil spring or the like and therefore any large variation in thepressing force during the operation of the key button can be eliminatedthereby ensuring an excellent operating quality.

In conclusion, the keyboard switch in accordance with the presentinvention, by virtue of the aforesaid advantages, has a significantindustrial value.

What we claim is:

l. A key board switch comprising a key button supporting framesupporting a plurality of key buttons movable vertically, horizontallydisposed tubular resilient means positioned under at least two keybuttons for interrupting vertical movement of said buttons and urgingthe same upwardly, printed substrate means positioned having pluralpairs of fixed electrodes corresponding to said buttons under saidresilient means, conductive resilient sheet means positioned betweensaid resilient means and said substrate means for protecting saidelectrodes from dirt and dust, insulating spacer means provided betweensaid substrate means and said conductive sheet means and having athickness and apertures respectively corresponding to said pairs ofelectrodes for allowing deformations of parts of LII said sheet meansand tubular means through the corresponding apertures to make parts ofsaid conductive resilient sheet means be in contact with thecorresponding pairs of fixed electrodes to shortcircuit the same, saidkey buttons having means for causing by downward actuations thereof saiddeformations of the conductive resilient sheet means and the tubularresilient means against their resilient forces, said resilient forcesenabling the respective means to release said deformations with releaseof said downward actuation of the key buttons to open the shortcircuitedelectrodes, and said tubular resilient means having the resilient forcefor causing a good feeling upon the actuation of said key buttons andabsorbing undesired possible actuations to said conductive sheet meansother than those caused by the actuations of the key buttons.

2. A key board switch as claimed in claim 1 wherein said conductiveresilient sheet means comprises continuous sheet-shaped conductiveportions provided at parts of said tubular resilient means which arelocated .opposite to said pairs of fixed electrodes.

3. A key board switch comprising:

a. a plurality of key buttons each having an actuating surface;

b. means for supporting said key buttons for independent movement in adirection normal to the actuating surfaces thereof;

c. an elongated conductive hollow resilient member extending along saidkey buttons adjacent said actuating surfaces;

d. an insulating substrate having a plurality of pairs of spacedcontacts affixed to a surface thereof, each of said pairs of contactsbeing spaced from the actuating surface of a corresponding key button,said resilient member being interposed between the actuating surface ofsaid key buttons and said pairs of contacts; and

e. insulating spacing means located on said substrate between each ofsaid pairs of contacts and between the surface of said substrate andsaid resilient member, displacement of one of said key buttons towardsaid insulating substrate deforming said resileint means toward the pairof contacts associ ated with the depressed button while being preventedby said spacing means from being deformed toward pairs of contactsassociated with buttons which have not been depressed.

4. A key board switch as defined by claim 3 wherein said elongatedhollow resilient member has a cylindrical cross-section.

5. A key board switch as defined by claim 4 wherein the thickness of thewall of said resilient member is thickest on the side facing theactuating surface of said key button.

6. A key board switch as defined by claim 3 wherein said elongatedhollow resilient member has a rectangular cross-section.

7. A key board switch as defined by claim 3 wherein said elongatedhollow resilient member has a triangular cross-section.

8. A key board switch as defined by claim 3 wherein said insulatingspacing means comprises a sheet having openings therein above each ofsaid pairs of contacts and said conductive resilient member is formedintegrally with said sheet.

1. A key board switch comprising a key button supporting framesupporting a plurality of key buttons movable vertically, horizontallydisposed tubular resilient means positioned under at least two keybuttons for interrupting vertical movement of said buttons and urgingthe same upwardly, printed substrate means positioned having pluralpairs of fixed electrodes corresponding to said buttons under saidresilient means, conductive resilient sheet means positioned betweensaid resilient means and said substrate means for protecting saidelectrodes from dirt and dust, insulating spacer means provided betweensaid substrate means and said conductive sheet means and having athickness and apertures respectively corresponding to said pairs ofelectrodes for allowing deformations of parts of said sheet means andtubular means through the corresponding apertures to make parts of saidconductive resilient sheet means be in contact with the correspondingpairs of fixed electrodes to shortcircuit the same, said key buttonshaving means for causing by downward actuations thereof saiddeformations of the conductive resilient sheet means and the tubularresilient means against their resilient forces, said resilient forcesenabling the respective means to release said deformations with releaseof said downward actuation of the key buttons to open the shortcircuitedelectrodes, and said tubular resilient means having the resilient forcefor causing a good feeling upon the actuation of said key buttons andabsorbing undesired possible actuations to said conductive sheet meansother than those caused by the actuations of the key buttons.
 2. A keyboard switch as claimed in claim 1 wherein said conductive resilientsheet means comprises continuous sheet-shaped conductive portionsprovided at parts of said tubular resilient means which are locatedopposite to said pairs of fixed electrodes.
 3. A key board switchcomprising: a. a plurality of key buttons each having an actuatingsurface; b. means for supporting said key buttons for independentmovement in a direction normal to thE actuating surfaces thereof; c. anelongated conductive hollow resilient member extending along said keybuttons adjacent said actuating surfaces; d. an insulating substratehaving a plurality of pairs of spaced contacts affixed to a surfacethereof, each of said pairs of contacts being spaced from the actuatingsurface of a corresponding key button, said resilient member beinginterposed between the actuating surface of said key buttons and saidpairs of contacts; and e. insulating spacing means located on saidsubstrate between each of said pairs of contacts and between the surfaceof said substrate and said resilient member, displacement of one of saidkey buttons toward said insulating substrate deforming said resileintmeans toward the pair of contacts associated with the depressed buttonwhile being prevented by said spacing means from being deformed towardpairs of contacts associated with buttons which have not been depressed.4. A key board switch as defined by claim 3 wherein said elongatedhollow resilient member has a cylindrical cross-section.
 5. A key boardswitch as defined by claim 4 wherein the thickness of the wall of saidresilient member is thickest on the side facing the actuating surface ofsaid key button.
 6. A key board switch as defined by claim 3 whereinsaid elongated hollow resilient member has a rectangular cross-section.7. A key board switch as defined by claim 3 wherein said elongatedhollow resilient member has a triangular cross-section.
 8. A key boardswitch as defined by claim 3 wherein said insulating spacing meanscomprises a sheet having openings therein above each of said pairs ofcontacts and said conductive resilient member is formed integrally withsaid sheet.